Electrical Overstress (EOS) is considered as the exposure of a device or an integrated circuit (IC) to a current or voltage beyond its absolute maximum ratings. EOS can occur due to voltage overshoots resulting in high destructive currents.
One type of EOS is Electrostatic Discharge (ESD), which is known as transfer of electrostatic charge between bodies or surfaces at different electrostatic potential. ESD can happen due to sudden discharge of charge from a charged body. The ESD occurs when differently-charged objects are brought close together or when the dielectric between them breaks down, often creating a visible spark. ESD is a high current event in the typical range of 0.1 A to 30 A in a very short period of time from 1 ns to 200 ns.
Another type of EOS relates to fast transient voltage surges. The most intense transient relate to lightning and industrial surges. Transient overvoltage events are usually of short duration, from several microseconds to a few milliseconds, but longer than ESD events. Transient voltage surges waveforms can be oscillatory or impulsive. The waveforms typically have a rising wavefront usually on the order of 0.5 μs to 10 μs. Transient over-voltages may range from 1 kV to 50 kV.
Transient voltage surges typically enter into the devices through power lines and may arise due to switching and lightning transients. Such power line transients may be produced on the power system due to events such as power outages, tripped circuit breaker, load switching, capacitor bank switching, equipment faults and others. Lightning events may directly inject high currents and produce over-voltages. However, lightning may also result in indirect effects. For example, lightning strikes may induce voltages/currents on the conductors outside and/or inside a building. Lightning may also impact ground current flows resulting from nearby direct-to-earth discharges coupling into the common ground paths of the grounding system of the device.
A surge protector (or surge suppressor) is a device designed to protect sensitive electrical devices from transient voltage surges. For example, a surge protector may be designed to limit the voltage supplied to an electric device by either blocking or by shorting to ground any unwanted voltages above a safe threshold. Accordingly, surge protection devices have characteristics or operating regimes beyond which they do not function as intended. However, improvements in operating conditions result in improved functionality that translates into higher profit margin and/or higher product revenue.